Re: [PATCH v4 1/5] iio: core: Handle 'dB' suffix in core

[Jonathan Cameron <jic23@kernel.org>]

On Wed, 29 Jan 2020 16:22:57 +0200
Beniamin Bia <beniamin.bia@analog.com> wrote:

> This patch handles the db suffix used for writing micro db values.
> 
> Signed-off-by: Beniamin Bia <beniamin.bia@analog.com>
> ---
>  drivers/iio/industrialio-core.c | 35 ++++++++++++++++++++++++++++++---
>  1 file changed, 32 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
> index 65ff0d067018..b70111837420 100644
> --- a/drivers/iio/industrialio-core.c
> +++ b/drivers/iio/industrialio-core.c
> @@ -769,17 +769,18 @@ static ssize_t iio_read_channel_info_avail(struct device *dev,
>  }
>  
>  /**
> - * iio_str_to_fixpoint() - Parse a fixed-point number from a string
> + * __iio_str_to_fixpoint() - Parse a fixed-point number from a string
>   * @str: The string to parse
>   * @fract_mult: Multiplier for the first decimal place, should be a power of 10
>   * @integer: The integer part of the number
>   * @fract: The fractional part of the number
> + * @scale_db: True if this should parse as dB
>   *
>   * Returns 0 on success, or a negative error code if the string could not be
>   * parsed.
>   */
> -int iio_str_to_fixpoint(const char *str, int fract_mult,
> -	int *integer, int *fract)
> +int __iio_str_to_fixpoint(const char *str, int fract_mult,
> +			  int *integer, int *fract, bool scale_db)
>  {
>  	int i = 0, f = 0;
>  	bool integer_part = true, negative = false;
> @@ -810,6 +811,10 @@ int iio_str_to_fixpoint(const char *str, int fract_mult,
>  				break;
>  			else
>  				return -EINVAL;
> +		} else if (!strncmp(str, " dB", sizeof(" dB") - 1) && scale_db) {

I think we need to ignore spacing between the value and the dB.

We could do that by ignoring spaces in general, but that will lead
to odd results in other cases.  Perhaps we just need to handle " dB" and "dB"
to cover likely options?

> +			/* Ignore the dB suffix */
> +			str += sizeof(" dB") - 1;
> +			continue;
>  		} else if (*str == '.' && integer_part) {
>  			integer_part = false;
>  		} else {
> @@ -832,6 +837,22 @@ int iio_str_to_fixpoint(const char *str, int fract_mult,
>  }
>  EXPORT_SYMBOL_GPL(iio_str_to_fixpoint);
>  
> +/**
> + * iio_str_to_fixpoint() - Parse a fixed-point number from a string
> + * @str: The string to parse
> + * @fract_mult: Multiplier for the first decimal place, should be a power of 10
> + * @integer: The integer part of the number
> + * @fract: The fractional part of the number
> + *
> + * Returns 0 on success, or a negative error code if the string could not be
> + * parsed.
> + */
> +int iio_str_to_fixpoint(const char *str, int fract_mult,
> +			int *integer, int *fract)
> +{
> +	return __iio_str_to_fixpoint(str, fract_mult, integer, fract, false);
> +}
> +
>  static ssize_t iio_write_channel_info(struct device *dev,
>  				      struct device_attribute *attr,
>  				      const char *buf,
> @@ -842,6 +863,7 @@ static ssize_t iio_write_channel_info(struct device *dev,
>  	int ret, fract_mult = 100000;
>  	int integer, fract = 0;
>  	bool is_char = false;
> +	bool scale_db = false;
>  
>  	/* Assumes decimal - precision based on number of digits */
>  	if (!indio_dev->info->write_raw)
> @@ -853,6 +875,9 @@ static ssize_t iio_write_channel_info(struct device *dev,
>  		case IIO_VAL_INT:
>  			fract_mult = 0;
>  			break;
> +		case IIO_VAL_INT_PLUS_MICRO_DB:
> +			scale_db = true;
> +			/* fall through */
>  		case IIO_VAL_INT_PLUS_MICRO:
>  			fract_mult = 100000;
>  			break;
> @@ -877,6 +902,10 @@ static ssize_t iio_write_channel_info(struct device *dev,
>  		if (ret)
>  			return ret;
>  	}
> +	ret = __iio_str_to_fixpoint(buf, fract_mult, &integer, &fract,
> +				    scale_db);
> +	if (ret)
> +		return ret;
>  
>  	ret = indio_dev->info->write_raw(indio_dev, this_attr->c,
>  					 integer, fract, this_attr->address);